In order to increase the data carrying capacity of LTE-A networks, the density of the network deployments should be increased to achieve higher cell-splitting gains. In such scenarios, co-channel interference from the neighboring cells 102a, 102b, as illustrated in FIG. 1, becomes a limiting factor for achieving higher network capacity.
In systems implementing Rel-11 of the LTE standards, such interference has been mitigated by using interference mitigation at user equipment (UE) 104 by accounting for spatial properties of interfering signals in a Minimum Mean Squared Error-Interference Rejection Combining (MMSE-IRC) receiver. In Rel-12, the performance of interference mitigation schemes at the UE was further improved by considering more advanced receiver algorithms. These more advanced algorithms were able to utilize additional information about the structure of interference (e.g. its distribution). For example, a receiver could estimate interference parameters such as a transmission mode, interference presence, modulation and precoding, etc. to facilitate interference cancellation and suppression at a symbol level using e.g. enhanced MMSE-IRC, maximum likelihood (ML) or symbol level interference cancellation (SLIC) receivers.
Another approach that has been introduced to increase capacity of LTE networks is multi user MIMO (MU-MIMO) schemes that facilitate simultaneous (concurrent) physical downlink shared channel (PDSCH) transmissions from an eNB to multiple UEs (using different layers) on the same time and frequency resources, as illustrated in FIG. 2. MU-MIMO has been defined in the LTE standards since Rel-8 (PMI-based TM5) and was further enhanced in Rel-9/10/11 (DMRS-based TM8/9/10). The simultaneous transmission of PDSCH in MU-MIMO on the same time and frequency resources introduces so called intra-cell interference between the layers designated to different UEs of the same cell. If there is insufficient spatial isolation between channels associated with the different UEs, the residual intra-cell interference may become a limiting factor on network capacity within the cell.